Pilgering rolling mill



July 11, 1933.

F. KOCKS Filed Feb. 16, 1951 atented Jul 11, 1933 UNITED, STATES PATENTOFFICE FRITZ ROCKS, OF DUSSELDORF, GERMANY, ASSIGNQR) TO THE FIRM VEREINIGTE STAHLWERKE AKTIENGESELISCHAFT, OF DUSSELDORF, GERMAN YPILGERING ROLLING MILL Application filed February 16, 1931, Serial No.516,161, and in Germany May 26, 1930,

The purpose of recent research has been to discover new processes forthe manufa c ture of seamless tubes with extremely thin walls, so as tomake them better able to compete with welded tubes.

The disadvantage of the pilgering methodwhich is the method exclusivelyadopt ed in Germany for the production of large seamless tubesis thatowing to the callbration hitherto employed it is not possible to reducethe usual thickness of-the walls of the tubes below the so-called normal'thlckness. This normal thickness and therefore the weight per metre ofthe tubes is so great i that the seamless tubes are in certain casesinterior from a commercial point of view to welded tubes which can beproduced with extremely thin walls.

The reason why it has not heretofore been I possible to produce a tubewith thinner walls than the normal thickness by means of the knownpilgering rolling mill calibration employed, is that in the form of passhitherto used the stretching operation-is effected al- 3 most entirelyby the bottom of the pass in the mout of the roll, whereas those partsof the pass extending to the sides of the pass contribute to the shapingonly to a slight extent. 1 Whereas the material being rolled is scarcelystretched at all at the sides .of the pass,

it has a very pronounced tendency at the bottom of the ass to flow inthe longitudinal'direction o the hollow body under hlgh locallyconcentrated roll1ng pressure. T he efiect is to distort the matenalvery considerably so that when the thickness of the walls is reducedbelow the normal, bursting and over-rolling occur at the bottom of thepass. 0 The invention-is diagrammat cally lllUS- trated in theaccompanying drawmg.

Fig'. 1 is a fragmentary detail section taken radially through one ofthe rolls shown n Fi 2. 5. %'ig. 2 is a longitudinal section through thebottom of a pilgering roll. I 3

Fig. 3 is a fragmentary cross section through the pass parallel to theplane 1n which the axes of the rolls he during the 0 working operation.

- The fact that in the known typesof pass it is chiefly the bottom ofthe pass that operates in the mouth of the rolls, is clear from thefactthat the cross sections in which the material is chieflysimultaneously rolled are ellipses or flat ovals, the major axes ofwhich lie in the gap between the rolls parallel to the axis of therolls. The material to be rolled is in the known pilger rolls as well asin that according to the invention shaped during treatment by the mouthof the pass in crosssections which lie at a certain distance parallelwith the line joining the centres of the rolls, because the shortestdistance, from roll surface to roll surface does not lie in the centreline but at a distance therefrom. As heretofore all the passes were soformed in the. roll that .in radial section through the, roll, forexample in the radial section 0 1' (Fig. 2), the known passes have asemi circular form with lateral bevelled parts or even flat ovals havingthe minor axis perpendicular to' the axis of the roll, it follows that asection, which is taken parallel to the line joining the centres 0 andof the rolls at a definite distance, for example the section A A (Fig.2) lying at the distance 0 from the line 0 0 is of flat elliptical oroval form that is quite inappreciable because half of the width of thepass at 2' is greater than the length A 2 representing the depth of thepass in the cross-section A A In other words,

the distance between the roll and the circular mandrel is at the bottomof the pass considerably less than atthe sides of the pass. The effectis that the roll, the material being rolled, and the mandrel are locallyoverstrained which makes it impossible to roll walls below the normalthickness. v

Furthermore, passes are known which, in radial section through the roll,are elliptical or of any flat-oval shape, such that the major axis ofthe ellipse lies parallel with the axis of the roll. and that thereforethe pass is not so deep as it is wide. Such formation ofthe pass has, aswill be understood, defects inherent in passes of circular radialcross-section hereinbefore described, but to an in creased degree,because the distance from roll a to mandrel in the cross-sections inwhich the main rolling operation takes place is considthe sides. Suchpasses thus stretch the material being 'rolled in a still more irregularmanner than passes which are circular in radial section and stress thematerial being rolled still more.

The object of the invention is so to form the pass that the pressure ofthe roll is distributed over the whole width of the pass, points ofrolling pressure at the bottom of the pass are avoided, and the materialbeing rolled is stretched as uniformly as possible over its Wholeperiphery. According to the invention the distances from the pass to themandrel in the cross-sections A A (Fig. 2) in which the principal workof rolling is car ried out, are the samein other words the shape of thepass in this cross-section is a circle with the diameter =A A (Fig. 3)and thus the material to be rolled is uniformly sretched. In order toobtain such a circular shape in the cross-section of the principal workof rolling, the pass of the pilgering mouth in radial sectionthrough'the roll according to the invention is given such an ellipticalor other oval shape that the major axis of the ellipse is perpendicularto the axis of the roll, the minor axis being parallel to it. Then thedesired circle can be obtained due to the fact that the length A 2 (Fig.2) is shorter than the depth of the passin the radial section 0 2' towhich the point 2' is belonging. The ellipticity of the ellipse (themajor axis of which is perpendicular to the axis of the roll) decreasesthen gradually from the beginning of the pilgering mouth to thebeginning of the polishing surface and the ellipse changes to a circleat the point of transition into the polishing pass.

In Figure 2, W denotes the roll, H the hollow body, D the mandrel andthe curve I the mouth, the are II the polishing surface, and the curveIII the outlet from th pass.

One condition of the invention is that the cross-section which at A A inFigure 2 is parallel to the line joining the centres 0 O and is shown inFigure 3, is circular without counting the lateral pass openings. Thisresults from the elliptical formation of the pass in cross-sectionthrough the roll (for example 0 1' in Figure 9.) so that half the majoraxis a, of the ellipse is equal to A 1 in Figures 1 and 2 and the minoraxis 27) of the ellipse is equal to B B.

As the cross-section A A in whiclrthe material being rolled is chieflyworked, moves gradually to the centre of the roll frame as the rollrotates and the'mouth' of the pass rolls over the material, theellipticity of the ellipse decreases from the first engagement by themouth up to the transition into the polishing pass until the radialsection through the roll in the polishing pass is circular.

I claim:

A roll pass for pilgering rolling mills, characterized in that the passat the mouth of the pilger is given such an elliptical shape in radialsection through the roll that the pass of the roll is circular in thecross-section which is perpendicular to the axis of the workat the pointWhere the principal rolling operation is carried out by the pass, theellipticity of the ellipse, the major axis of which is perpendicular tothe axis of the roll, decreasing continuously from the beginning of thepilgering mouth to th beginning of the polishing surface and the ellipsechanging to circular shape on the transition into the polishing pass.

FRITZ KOCKS.

